Endless conveyor belts can be made, ends of belts can be joined, and conveyor belts made of rubber and equipped with stress bearing inserts can be repaired by providing a conveyor belt section with rubber material, preparing it for vulcanization, bringing it between heatable press platens and vulcanizing it using heat and pressure.
The rubber material provided to the conveyor belt section has Newtonian flow properties and the conveyor belt section undergoes a flow-producing hot pressing.
By "rubber material" we mean natural rubber and synthetic rubber including plastic or synthetic resin material as well.
A pressurized hot pressing is required in the vulcanization of the conveyor belt and/or on the conveyor belt so that the rubber mixture to be vulcanized fills all the hollow spaces in the structure of the conveyor belt section to be vulcanized and the enclosed air, also steam or water vapor released from moisture in the material used, can escape.
Pressure and temperature can be appropriately selected for the materials used. For example the temperature can be in the vicinity of about 150.degree. C. Different vulcanization stages can be distinguished in the vulcanization of the rubber material. In fact the vulcanization is a cross-linking reaction in which the macromolecules of the rubber material are connected with each other by cross-linkages.
In the nonvulcanized state the rubber molecules are not fixed in position with respect to each other and can move about more or less freely. The rubber material is, particularly in the melt, plastically flowable or deformable. It has mechanical and thermodynamically irreversible Newtonian flow properties.
Currently during vulcanization the conveyor belt section between press platens moveable up and down but otherwise fixed is only acted on by a static pressure which acts perpendicularly to the plane of the conveyor belt section and for a sufficient duration.
To guarantee that all hollow spaces are filled satisfactorily pressures are required between 10 to 15 bar and correspondingly heavy presses. That is troublesome particularly when a mounting press is involved which is used on the working site to make an endless conveyor belt, e.g. for a mine for coal, lignite, ore, gravel or the like. For vulcanizations in which a hot pressing is not required in view of chemical effects considerably reduced pressures can be used, e.g. pressures between 3 and 5 bar.